1. Field of the Invention
The present invention relates to an image pickup lens system and an image pickup apparatus, and more particularly to an image pickup lens system suitable for use in a small-size camera such as a camera for video telephone on a cellular phone or a camera for video conference on a laptop personal computer, for example, the image pickup lens system having a wide angle of view capable of capturing images in a portrait image capturing range and also having a good focusing capability up to a peripheral image region, and an image pickup apparatus incorporating such an image pickup lens system.
2. Description of the Related Art
There have been proposed image pickup lens systems for use with an imager such as a CCD (Charge-Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor) used in small-size cameras. The proposed image pickup lens systems employ plastic lenses rather than glass lenses and include a small number of lenses for a reduced cost and a compact size.
It has heretofore been necessary for such image pickup lens systems to be constructed as an optical system with aberrations appropriately corrected to reduce the optical length of the lenses and achieve good image quality for the purpose of reducing the size of cameras incorporating such image pickup lens systems therein.
Many image pickup lens systems employing two plastic lenses in two groups have been invented and reported as disclosed in Japanese patent laid-open Nos. 2004-62014 and 2004-177976. The image pickup lens system disclosed in the former publication includes a positive lens and a negative lens, and the image pickup lens system disclosed in the latter publication includes a positive lens and a positive lens.
In recent years, since small-size cameras have been finding a wide variety of applications including a camera for video telephone on a cellular phone and a camera for video conference on a laptop personal computer, there has been a demand for small-size cameras with a wide angle of view capable of capturing images in a portrait image capturing range.